This invention relates generally to heat exchanger coils and, more particularly, to an apparatus for transporting long plate fin heat exchanger coils between stations during production.
A plate fin heat exchanger coil is commonly constructed with a plurality of flat, parallel plates having laterally spaced holes therein for receiving refrigerant tubes, or hairpin tubes, therein. At each end of the plate fin bundle, there is a tube sheet composed of heavier material, and adjacent one of the tube sheets, generally the upper tube sheet, the open ends of the hairpin tubes are fluidly connected by way of U-shaped return bends that are secured thereto by way of soldering, brazing, or the like. When the coils are installed into a refrigeration system, the refrigerant is made to flow through the hairpin tubes, and the air to be cooled or heated is made to flow over the plate fins, such that a heat transfer is thereby affected.
Typically, the production of plate fin coils involves manual assembly and transport. Small coils are lifted by hand and large coils are moved between stations by crane. The use of cranes is time consuming and clumsy, but tends to protect the delicate fins from damage, since lifting is done by the tube sheets. Conveyors would work for short distances and short coils, but fins tend to sag onto the conveyor in longer coils.
In U.S. Pat. No. 4,228,573 which issued to Barnard, there is disclosed an automated machine for manufacturing fin plate heat exchangers of the type suitable for use in air conditioning systems. Each unit, as it is being assembled, is retained within a holding fixture with the tube receiving holes of the retained fin pack being supported in a generally horizontal position. Initially, the perforated fins and one perforated tube sheet or header are placed in the fixture and then clamped in place using a pair of jaws that are adapted to swing upwardly into locking engagement against the perforated end faces of the partially assembled unit. The fixture is then passed through a series of processing stations wherein the hairpins are laced into the package, a second header is inserted over the laced tube ends and finally the tubes are expanded into locking contact against the surrounding elements.
The fixtures containing the retained units in the Barnard device are carried between processing stations on a conveyor belt. At each processing station, the fixture is lifted from the belt and carried to a remote position wherein a specific manufacturing step is carried out. Upon the completion of the operation, the fixture is again returned to the conveyor belt and moved to the next subsequent station. Because of the inherent weight of the heat exchangers, they tend to sag in the middle and the fins are damaged as they rub against the conveyor. Further, the timing of the various operational steps in Barnard is not coordinated and, in order to avoid bottlenecks along the line, fixtures containing partially assembled units are moved to temporary overhead storage areas where they are held until needed. As a consequence, each fixture must be loaded and unloaded from the main conveyor a number of times before the assembly operation is completed. This excessive handling slows down the automated process and raises the unit cost of the assembled units. The apparatus needed to carry out the many handling and processing steps is also relatively complex and difficult to maintain.
A further disadvantage associated with the Barnard machine concerns the excessive handling of the coils. During a number of assembly operations, the clamps must be lowered so that the operation can be completed. This, of course, releases the unit from the fixture at a time when it is being worked upon. As a consequence the fin plates can become misaligned or damaged and, as a consequence, the unit may eventually have to be scrapped.
It should be noted that in Barnard, at each station, the coils are lifted by a crane and held in a predetermined position while the operation at the station is performed.
Thus, there is a clear need for a conveyor system for moving coils from one location to another during assembly that provides quick and accurate coil location at various stations while protecting the coil from damage and provides an apparatus for supporting and moving the coil while at a processing station.